Pyrolysis of mixtures containing tribromofluoromethane



3,033,905 PYROLYSIS F MIXTURES CONTAINING TRIBROMOFLUOROMETHANE Leo A. Wall, Washington, D.C., and Walter J. Pummer,

Rockville, Md., assignors to the United States ofAmerion as represented by the Secretary of the Navy No Drawing. Filed Oct. 30, 1955), Ser. No. 849,991 8 Claims. (Cl. 260-650) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to the preparation of aromatic fluorocarbons from the pyrolysis of a mixture of substitution products of methane and more particularly to a method for increasing the poor yield of certain aromatic fluorocarbons resulting from the pyrolysis of tribromofluoromethane by itself.

It is known in the art that hexafluorobenzene can be produced by the pyrolysis of tribromofluoromethane alone and that among the by-products of this sythesis are pentafluorobromobenzene in fair yield and traces of perfiuorotoluene. These latter compounds are of particular interest since from these compounds derivatives contain- I ing one or two functional groups may be prepared. These derivatives in turn Will serve as intermediates for further syntheses. As an example, pentafiuorobromobenzene readily forms a Grignard reagent from which a variety of derivatives may be synthesized.

At present pentafluorobromobenzene can be produced Table I.Pyr0lysis of Mixtures Mixtures Weight, Moles Temp, Pressure,

g. C. p.s.i.

1% 540 205 4. .5 1,100 as l 545 -1 500 150 4,005 15 759 500 150 g}; g 540 150 3,400 12.5 1,300 8.5 l

3,033,265 Patented May 8, 1962 Flow, Time, 'Recd 13m, Mixtures cc./ hr. perper- Products, g.

cent cent 3 S4C0Fe 25 5 77 68 420 210 CFBrs 126 Residue 9.5 CaFs 50 ll 49 416 197CFB1'3 I 210 Residue e Combined and distilled together. b Product distribution similar to Table II. Does not include the added bromine.

Table II.Distillation of CFBr /CBr Mixtures Boiling Pressure, Weight, Fraction p piionz, mm. 1;. Products 1 25-90 700 139 011. 1 (80%), CFBrCFBr (10%), CFzBIZ. 2; 90420 760 848 C;6BraB-(90%), CsFzBrn.

. v 1.1 r. 3 120-145 760 160 CaFsBr (79%), "CzF Bn A 1, 131. t 4 .85- 25 218 csFlBn (90%), CzFzBn Calls 1. 5 88-98 10 61. 5 oaFiBrz (50%), C213 (10%). 6 10 268 Not analyzed.

Table [IL-Distillation of CFBr /CF CBr Mixtures Boiling Weight, Fraction pgit, g. Products 50-95 51.2 C121 (66%), C F Br (20%), CeFsCF; 95-106 51.1 crumkssw, 0.1 8011%), 0.11 601%). 106-110 302. 9 CFBra (90%), C7Fg (5%), CzFsBls (4%) 110 401 Not analyzed.

Table I V.--Distillati0n of CFBr /CHBr Mixture Boiling Weight, Fraction pgit, g. Products 45-100 09.4 01m (70%), OFHBrz (2 100425 510.4 CFBra (90%) CgFBl's. -140 09.1 CaFsBr (60%), CHBr-s 30% 011 1131,

CBFlBlH. -175 39. 7 C4F3Bl3, CaFaBra, CsFvBr. 5 -200 94.8 COF4Br2, CgFqBll.

Though the lowest pressure employed in the pyrolyses of Table I Was 50 psi. similar pyrolyses have been conducted at pressures as low as atmospheric in which case a temperature of about 640 C. was required to effect the synthesis.

Although hexafiuorobenzene is obtained in all the mixed pyrolyses, the overall composition of the products is such that the yields of desirable derivatives have been increased markedly over that composition resulting from the pyrolysis of tribromofluoromethane alone. As an ex ample, in Table II, the yields of pentafluorobromobenzene (Fraction #3) and dibromotetrafiuorobenzene (Fraction #4) have been increased by 15 and 25 percent, respectively, from that obtained by the pyrolysis of trib'romo- 7 fluoromethane alone. Also, in Table 111 instead of showing up as mere traces as in the case of the pyrolysis of tribromofluoromethane alone the yield of perfluorotoluene has been increased to 14 percent based on the 1,1,1-trifiuorotribromoethane added to the CFBr is particularly pronounced in view of the dilution ratio of about 10:1 as compared to the other dilution ratios of about :1.

The inventors attempted to prepare pentafiuorobenzene by the mixed pyrolysis'of CFBrand CHBr but as is shown by Table IV the results'were not those expected.

the pressure was allowed to dissipate. After cooling the resultant composition was washed with aqueous sodium The predominant amounts of bromo fiuoro compounds indicates that. hydrogen bromide was more easily removed than free bromine which is produced during the formation of both pentafiuorobromoben'zene,and perfluorotoluene.

water. I

As shown in Table I amixture of CFBr and bromine were pyrolyzed, however,-because of the adverse effect of the excess'bromine upon the course of the reaction the yield of hexafluorobenzene decreased rapidly.

A mixture of CFBr and CF Br were also pyrolyzed but the product yield of other than C F was not of sutficient significance to warrant further investigation.

These pyrolyses 'were conducted in apparatus made of metal with copper tubing and fittings and a stainless steel reservoir. The mixture to be pyrolyzed was placed in the reservoir and the platinum furnace tube was heated to the temperatures shown in Table I. An inert gas under pressure was then admitted to the system and a flow" was established to serve the purposes of placing the reaction under pressure, of carrying the reactants into the furnace during the synthesis. Although nitrogen (prepurified) was usually employed, other gases such as helium or argon can be substituted. When the reaction was completed 4.5 'tube and lastly, of carrying away the bromine .formed- I bisultite solution, then with 5% sodium hydroxide solution and, finally, with water. The liquid was dried and then distilled resulting in the fractions shown in Tables II, III, and IV.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The production of aromatic fluorocarbons by the pyrolysis of a mixture composed of CFBr and a material selected from the group consisting of CBr Cl-lBr and CF CBr at a temperature of about 540 C. to 640 C. and at a pressure of from atmospheric to about 265 p.s.i.

2. The production of C F Br by the pyrolysis of a mixture of CFBr and CBr at a temperature of about 540 C. and a pressure of about 265 psi.

3. The process recited in claim 2 in which the mixture to be pyrolyzed contains approximately 5 moles of CFBr for each mole of CHBI I 6. The production of C F CF by the pyrolysis of a mixture of CFBr and CF CBr at'a temperature of about 560 C. and a'pressure of about p.s.i.

7. The process recited in claim 6 wherein the mixture to be pyrolyzed containsapproximately 10 moles of CFBr 'for each mole of CF CBr 8. The production of aromaticlluorocarbons by the pyrolysis of a mixture composed of CFBr and a material selected from the group consisting of CF CBr CHBr and CBr at a temperature of about 540 C. to 560 C. and 4.o

at a pressure of about .50 p.s.i. to 265 p.s.i.

References Cited in the file of this patent IJNITED STATES PATENTS 2,927,138 H ,Wall et al, Marll, 1960 OTHER REFERENCES Acad. Roy. Belg, vol.4l 

1. THE PRODUCTION OF AROMATIC FLUOROCARBONS BY THE PYROLYSIS OF A MIXTURE COMPOSED OF CFBR3 AND A MATERIAL SELECTED FROM THE GROUP CONSISTING OF CBR4,CHBR3 AND CF3CBR3 AT A TEMPERATURE OF ABOUT 540* C. TO 640* C. AND AT A PRESSURE OF FROM ATMOSPHERIC TO ABOUT 265 P.S.I. 